Scientists across China and the United States collaborating on the PandaX search for dark matter from an underground lab in southwestern China report results from the first stage of the experiment in a new study published in the Beijing-based journal Science China Physics, Mechanics & Astronomy.

PandaX is the first dark matter experiment in China that deploys more than one hundred kilograms of xenon as a detector; the project is designed to monitor potential collisions between xenon nucleons and weakly interactive massive particles, hypothesized candidates for dark matter.

In the new study, scientists explain, "Dark matter is a leading candidate to explain gravitational effects observed in galactic rotational curves, galaxy clusters, and large scale structure formation."

"Weakly interacting massive particles (WIMPs), a particular class of dark matter candidates, are interesting in particle physics and can be studied in colliders [and in] indirect and direct detection experiments."

If confirmed, dark matter particles would extend understanding of the fundamental building blocks of nature beyond the Standard Model of particle physics, and would provide support for theories on supersymmetry and extra dimensions of space-time.

"Direct positive detection of WIMPs using ultra-low background detectors in deep underground laboratories would provide convincing evidence of dark matter in our solar system and allow the probing of fundamental properties of WIMPs," they add in the new study.

Direct detection experiments using different technologies have produced many interesting results, but not universally confirmed evidence of weakly interacting massive particles. These results have produced much excitement across the global scientific community and call for further examination of WIMP signals through other experiments.

"In recent years, new techniques using noble liquids (xenon, argon) have shown exceptional potential due to the capability of background suppression and discrimination, and scalability to large target masses," state the PandaX collaborators. "The XENON10/100 and LUX experiments using the dual-phase technique have improved WIMP detection sensitivity by more than two orders of magnitude in a wide mass range."

China's PandaX experiment, operated at the China Jinping Underground Laboratory, uses the dual-phase xenon technique to search for both low and high mass WIMP dark matter.

The initial success of the PandaX project demonstrates China has joined the global competition at the scientific frontier marking dark matter searches.

Today more than twenty dark matter search experiments are being conducted worldwide. Many dark matter search experiments, such as the DAMA/LIBRA experiment in Italy, the CoGeNT and CDMS experiments in the US, and the German-led CRESST experiment have reported findings that could be interpreted as positive signals of dark matter in recent years.

The PandaX collaboration joins this effort with results from a dark matter search that started in May of 2014.

No dark matter signal was observed in the first PandaX-I run, which places strong constraints on all previously reported dark matter-like signals from other similar types of experiments.

The PandaX experiment to date has collected about 4 million raw events; only about ten thousand events fell into the energy region of interest for dark matter. In the quiet central part of the xenon target only 46 events were observed.

However, the data from these 46 events was consistent with signals marking background radiation, not dark matter.

PandaX stands for Particle and Astrophysical Xenon Detector. The experiment is being conducted by an international team of about 40 scientists, and led by researchers from Shanghai Jiao Tong University.

The goal of the first stage of PandaX experiment is to examine previously reported dark matter-like signals. The scale of the PandaX-I experiment is second only to that of LUX, which is currently the planet's largest dark matter experiment and is located in a South Dakota mine in the US.

To shield the Chinese experiment from cosmic rays, the PandaX detector is located at the China Jinping Underground Laboratory (CJPL), the deepest underground laboratory in the world. CJPL was developed by Tsinghua University and the Yalong River Hydropower Development Company in 2010.

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39 comments

Let me draw a picture of why experiments looking for dark matter on Earth are coming up dry. Hypothesize that dark matter, whatever it is, interacts weakly* with neutrinos. The shape of dark matter around galaxies gives a rough range for the interaction--strong enough that supernovas and other neutrino sources balance gravity at some distance from the galaxy center.

The sun is also a neutrino source. Not nearly as strong as supernovas, but then again we are a lot closer to the sun. So supernovas provide the muscle to keep dark matter away from the Earth, and solar neutrinos sweep up any dark matter left.

Result? No dark matter is found in experiments on Earth, since there is no dark matter near Earth. Solution? Make dark matter particles at CERN, or spend decades sending a dark matter detector light days from the sun.

Lets assume you detect "something" new. How to statistically prove to FIVE SIGMA that science requires to narrow down a discovery, that this new "something" is indeed the fabled DM?

DM will not be distributed evenly in the galaxy, due to gravitational wakes I've discussed earlier, among other effects.

1, You would need to do statistical models on the galaxy and it's close neighbors, and model the region of stars around the solar system and all known massive objects in the Solar System, to see what the pattern of gravitational wakes would/should be, to understand if and when the highest occurrence of DM particles should be. (conjecture is it would be correlated to the orbits of Jupiter and Saturn, but complex systems can produce unexpected results).

2, Explain why it doesn't collect over time and alter the mass/apparent mass of solar system objects as it should. After all, that's allegedly what it does in terms of rim stellar orbit

3, Explain why we don't experience a "pogo" effect, as slow moving gravitational wakes should be "captured" by the Sun, Jupiter, and Saturn, and should go into some sort of complex linear, circular, or horseshoe orbit. These phenomena would perturb planets and moons, and would asymmetrically perturb the apparent surface gravity of the Earth, which would be noticed immediately by GRACE and NIST.

4, If 100kg of of a Noble Gas in liquid is expected to accumulate a statistically significant number of DM collisions over human timescales, why hasn't the much denser core of the Earth grown in accumulated DM mass over the ~4.56Gy that it is supposed to have been here? A static collision, rare as it may be on a per-volume basis, would slow the particle to below escape velocity, and trap it permanently within the Earth's gravitational field.

If there is 4 times as much DM as Ordinary Matter, the Earth should be much more massive than it is, even if only a fraction of particles are captured.

Lets see how can we statistically prove to FIVE SIGMA that Lrrkrrrr is a loon?

3, Explain why we don't experience a "pogo" effect, as slow moving gravitational wakes should be "captured" by the Sun, Jupiter, and Saturn, and should go into some sort of complex linear, circular, or horseshoe orbit. These phenomena would perturb planets and moons, and would asymmetrically perturb the apparent surface gravity of the Earth, which would be noticed immediately by GRACE and NIST

-There. That was easy wasn't it? Lrrkrrr thinks the solar system is a lake with motor boats in it.

Lets see how can we statistically prove to FIVE SIGMA that Lrrkrrrr is a loon?

Observable mass within our solar system, and other nearby solar systems, exhibit a 1:1 ratio of mass to gravity. This means there is no unaccounted mass to justifying a 4:1 mass/gravity ratio presumed for DM, and DM isn't necessary to explain gravitational lensing. I didn't need the differential equations in Einstein's GR thesis whereby he proved the Laws of Gravity & Energy, making it simple for even grade school children to understand.

So far, the entire DM debate is phantom science chasing phantom silliness because it gives some people something to think about while they're daydreaming during the day or while trying to go to sleep at night.

Oh dear, that altogether precludes WIMP models and requires that dark matter convert to stars and luminous matter in high density regions of galactic cores, globular clusters, and in giant molecular clouds in particular where gravitationally-bound cold-dark-matter (CDM) Bok globules on their disk-crossing halo orbits can get trapped and become visible (opaque) with gaseous stellar metallicity.

Otherwise, Bok globule stellar metallicity is condensed (sequestered) into icy chondrules at bitterly-cold temperatures of around 10 Kelvins, leaving nearly-invisible helium and molecular hydrogen as the reservoirs of CDM in galactic halos.

Oh dear, that altogether precludes WIMP models and requires that dark matter convert to stars and luminous matter in high density regions of galactic cores, globular clusters, and in giant molecular clouds in particular where gravitationally-bound cold-dark-matter (CDM) Bok globules on their disk-crossing halo orbits can get trapped and become visible (opaque) with gaseous stellar metallicity.

.......and you've been out there to record the presence of all the observable matter, and calculate its gravity fields? Then voila, you must be a "god" because you've been some place no man can ever go & that's how you know all this stuff? I'd suggest you download a copy of Einstein's GR and study the sections of his Differential Equations & other math that pertains to gravity like I've done, then come back here & try to give this Nuclear/Electrical Engineer lectures on science. You are simply an expert in "Trekkie phantom science". (beam this guy up Scotty).

slow moving gravitational wakes should be "captured" by the Sun, Jupiter, and Saturn... These phenomena would perturb planets and moons

"The average density of dark matter near the solar system is approximately 1 proton-mass for every 3 cubic centimeter... for an orbital radius of 100 million km, we get a total of 2.3x10^12 kg of dark matter within the Earth's orbit. This sounds like a lot, but the sun's mass is 2x10^30 kg. All of that dark matter only weighs 10-18 as much as the sun does, so we cannot detect the tiny pull of dark matter upon the Earth's orbit. The same story is true all over the solar system: the gravitational pulls of the sun and planets are always much larger than that of the dark matter"

-Not to mention that DM inside the system would be subject to the same orbital mechanics as the planets. And so the planets would not be moving through DM, but with it.

"Now consider the effect of dark matter upon the orbit of the sun around the galactic center. Let's suppose that the density of the dark matter is the same everywhere in the galaxy; this is NOT true (the density is much higher near the galactic center), so the dark matter mass will really be higher than we calculate.

"The radius of the sun's orbit is about 2.5x10^17 km, so the total mass of dark matter within that orbit is 6x10^40 kg. This is the mass of 3x10^10 (30 billion) stars like the sun! The entire galaxy only contains ~100 billion stars, so the dark matter does have a significant effect on the sun's orbit through the galaxy. For objects farther out near the edge of the galaxy, the dark matter is actually the main thing keeping them in their orbits. This is more or less how dark matter was discovered..."

"In other words, a galaxy is much lower in density than the solar system, so the small dark matter density becomes much more important."

..........Scotty, beam this Ghosty guy back to earth, he thinks he's a spirit god who's been there and knows all about where the "dark stuff" is because he knows more differential equations than Einstein ever knew.

..........Scotty, beam this Ghosty guy back to earth, he thinks he's a spirit god who's been there and knows all about where the "dark stuff" is because he knows more differential equations than Einstein ever knew.

..........Scotty, beam this Ghosty guy back to earth, he thinks he's a spirit god who's been there and knows all about where the "dark stuff" is because he knows more differential equations than Einstein ever knew.

-an actual physicist. Now why on earth would you think I made them up myself? I really need you to answer this question benny

Oh, I get it, he's your Ghosty god who's been buzzing around the universe promoting faith in the phantom science for which you're unable to come up with any math? The faith it must take to believe in your eschatological science is just overwhelming this Nuclear/Electrical Engineer. Got any bible verse you'd like to start quoting for a good followup?

1, orbital radius of Earth 153million km, not 100 million.2, You erroneously assume that only material which starts out within that radius matters. Obviously DM from inter-stellar space would be attracted to the the point where the sum of all gravitational vectors is pointing, which is usually the nearest star. This means that about 3 or 4 solar masses worth of Dark Matter should have been collected by the Sun, the planets, and dwarf planets.

3, Make fun of the "wake" concept, but you are ignorant of how objects moving through a fluid or a cloud leave a tail wake, then? Are you also ignorant of how planets moving through dust, which don't capture all of that dust, can throw it on hyperbolic trajectories (relative to themselves), which in about half the cases would mean the (DM) would be thrown inward, and other half the cases it might be thrown outward (but recaptured if not exceeding SS escape velocity).

For starters, you didn't know the radius of the Earth's orbit... Yeah, those facts make me fully convinced that you are unqualified, because you don't even have an introductory knowledge of the concept being discussed

FOR STARTERS you didnt realize that I was quoting a PHYSICIST you fucking MORON. Do you see how deranged you are??

But of course, you are incorrectly using a less dense value than would be needed for the 4 to 1 ratio within galactic space.

How dense is a six-winged-three-toed-five-headed-eight-armed-four-faced-intersolar-archangel? I hope you added in all the mass he is tugging through the main traffic channels of the Milky Way midstream, other the wise, your ciphering may be off by a factor of negative 1000.

The interstellar hydrogen isn't collected because of the BOW SHOCK and the RADIATION PRESSURE, which DO NOT EFFECT THE HYPOTHESIZED DARK MATTER.

This is basic stuff man.

The BOW SHOCK is a WAKE caused by the various forms of the EM force interacting with the inter-stellar media which we are moving THROUGH.

Various media in the local space in the galaxy are not perfectly synchronized in any direction. The sun and other stars pass one another by at a few kilometers per second, as do dust/gas clouds, and as would DM clouds. The BOW SHOCK proves the matter is not synchronized, and comes from many different vector sources. One reason for this may be the fact we are interacting with the L and S Magellanic clouds, as well as colliding or close to colliding with a few Dwarf Galaxies.

Also, even otherwise "Stable" orbits of stars and gas clouds can cross paths, therefore your position is wrong regardless. Look at Pluto/Neptune, or any meteor shower for goodness sake.

"...for an orbital radius of 100 million km, we get a total of 2.3x10^12 kg of dark matter within the Earth's orbit. This sounds like a lot, but the sun's mass is 2x10^30 kg. All of that dark matter only weighs 10-18 as much as the sun does, so we cannot detect the tiny pull of dark matter upon the Earth's orbit. The same story is true all over the solar system: the gravitational pulls of the sun and planets are always much larger than that of the dark matter"

-The solar system is enveloped in DM which is traveling at roughly the same orbital velocity. It is not traveling THROUGH anything. And any DM within the system is tending to follow the same orbital paths as the planets. Because DM is gravitationally bound.

What makes you think it would just be sitting there? Its orbit around the galactic center is dragging the stars around with it which is why the outer stars are traveling faster than they are supposed to.

The interstellar hydrogen isn't collected because of the BOW SHOCK and the RADIATION PRESSURE, which DO NOT EFFECT THE HYPOTHESIZED DARK MATTER

But it would still be traveling at the same velocity as the solar system. Again, why would you think it wasnt orbiting the galactic center like any other gravitationally-bound material?

This is basic stuff man.

If gravity was able to suck in interstellar stuff why wouldnt the solar system have a halo of H2 around it? Perhaps it does. But not enough to affect anything. And this halo would be orbiting the sun. Wouldnt it?

What makes you think it would just be sitting there? Its orbit around the galactic center is dragging the stars around with it which is why the outer stars are traveling faster than they are supposed to.

FIX YOUR MATH.

I can show you math, and a diagram, which describes using only ordinary matter objects why stars on the outside of galaxies travel faster than they are "supposed to".

The correct N-body for the stellar mass produces a Acceleration curve which when plotted with radius on the X-axis and A on the Y axis is concave upward (after leaving the galactic core). Which is to say.

At 0 it's small(ignoring the black hole itself) then it grows to a peak, then it bottoms out around 1/3 of the peak and stays approximately flat for about 1/3rd of the radius of the galaxy, and then it grows again as you get outside the galaxy.

This can be shown for a very simple N-body I've been working on earlier today. I can take a photo of my hand work and put it on youtube.

The interstellar hydrogen isn't collected because of the BOW SHOCK and the RADIATION PRESSURE, which DO NOT EFFECT THE HYPOTHESIZED DARK MATTER

But it would still be traveling at the same velocity as the solar system. Again, why would you think it wasnt orbiting the galactic center like any other gravitationally-bound material?

This is basic stuff man.

If gravity was able to suck in interstellar stuff why wouldnt the solar system have a halo of H2 around it? Perhaps it does. But not enough to affect anything. And this halo would be orbiting the sun. Wouldnt it?

The Bow Shock deflects the slower-moving gas so that it goes around the sun, and most of it never enters the solar system.

It works just like a boat on the water, hence the name "Bow Shock".

To answer your question more completely, many, many objects and systems in the Galaxy do not have stable galactic orbits, and are decaying inward, thus they do not move together at the same speed, but vary by a few km/s

The reason this happens is that for arbitrary disk of matter, due to the inverse squared law, any ring outside of a sub-ring has a net attractive force to the outside (unlike the shell theorem applying to a sphere), because it is easy to see that a given object is attracted much more strongly to a star that is one ring outside itself and is adjacent to itself, than it is to a star on that same outside ring anywhere else on the ring.

What this means is outer rings of matter in a galaxy actually decrease the net inward acceleration of inner rings, slowing them down. However, as you approach the last few "rings" in your system, the outer rings have nothing outside themselves to slow them down, thus they orbit at a "simplified" velocity where virtually all other matter in the galaxy is pulling them inward, thus their stable orbital velocity is higher. For the outer 1/3rd it is possible for their stable orbital velocity to be 2 times as high as the middle 1/3rd: observed a few times.

According to NASA, the SUN is moving about 20km/s relative to the stars in it's neighborhood,and if you look at Proxima Centauri, it says it's proper motion is 21km/s (via Radial Velocity).

Wait now, I knew about Planetary Migration like 3/4 of a lifetime ago, when I was 8 years old, so don't try that one on me guy. A different form of Gravitational Wake is involved in planetary migration, typically involving Gas Giants migrating inward while ejecting smaller planets from the system. This model is used to explain the existence of "Hot Jupiters", but planetary migration in general, I've definitely known about it and been interested in it for 20-something years.

Try again, because I did not have to look it up. I was given a book on the Voyager mission when I was about 7 or 8 years old, whatever it was.We've learned alot since then, but that's beside the point. I didn't have to look anything up, because I knew what it was; except Saturn's semi-major axis, that I looked up...

But it would have to be wrong because youre assuming for some reason that DM is stationary. Its not.

........and you know this because you've spread your ghosty angel wings & went out there & checked it out yourself? To have faith in tripe like this statement only proves a sucker is born every second, and you're just one more of them, someone who's never seen a Differential Equation you could solve who has become an expert in GR. You must be another classmate in Ira's special education class where he's learned those mathless "different equations".

If you want to know why some "halo" stars appear to be orbiting at "impossible" speeds, it is because of the approximately 1/3, 1/3, 1/3 distribution I described there.

In fact, for stars in the middle 1/3 of the radius, I literally got net acceleration vectors which were identical in two cases, and approximately identical across the entire middle 1/3rd, varying by a factor of only about +/-1 part per 16 units of acceleration.

This model used no Dark Matter, and simulated a "Dwarf Galaxy" where ~1/3rd of the mass was contained in the inner 5% of the radius.

It produced a curve which is nearly identical to what is observed, using only stellar bodies AND decreasing average density as you go out from the center, as most real galaxies are not perfect disks by thin out some near the edges in terms of stars and gas.

The fast halo star is correctly predicted by the Newtonian N-Body, without the need for Dark matter.

you know this because you've spread your ghosty angel wings & went out there & checked it out yourself?

No retard because it is gravitationally bound. Why wouldn't it?

You whose gray matter has been replaced by dark matter..........you can't prove this because you can't demonstrate how gravitational attraction between bodies can have distinctly identifying flavors of gravity which can in some way segregate & thus uniquely clump one kind of matter while excluding another. But I guess your old age dimentia has convinced you that as long as you can think it's real, then Einstein must be wrong,

Hey, ever seen a differential equation you could solve? Now you know what your problem is in your old age......you've retired in the wrong place, science is not your forte.

Many local community colleges offer discount tuition for retired seniors like yourself. I'd suggest you head over to yours & enroll in a math course & learn what it takes to really comprehend the language of science. For you, I'd guess you start with high school algebra & not the differential equations in Einstein's GR because at your level of mathematical comprehension you can't discern the difference between a "complex integral" & a "differential equation".

And by the way, stay away from quoting those bible verses, those numbers at the start of those verses have nothing to do with the math you keep screaming for other people to learn. I just noticed there's a new article here at PhysOrg about restoring memory loss associated with Alzheimer's, you should check it out & maybe you can get some help in your new math class with Ira.

Boolean Algebra is a course I had in Computer Science, but this "Boogers" or "paste", never heard of that math, maybe some memory loss reversal really would help refresh your mental state, but keep away from those bible verses.

@benni and the tardssorry, mr NOOclear engineer... I find it hard to believe that you took computer science when you could not figure out how to talk to the mods/admin using a link at the bottom of every page on Phys.org... and then told everyone that since you couldn't PM I couldn't talk to the site admin/mods

Then there is your ignorance regarding Phishing and how people can steal your personal information... which you give away freely just by being here- can you say cookies?

Oh! I get it now!You think computer cookies are the flavor of Gravity?

You never heard of it till you just read it in my post. I have serious doubts you'd ever heard of Differential Equations until I started making references to them in Einstein's GR, and you to this day still can't identify the branch of math with which to identify them unless you had WikiPedia & my challenges for you to look it up.

@benni and the tardssorry, mr NOOclear engineer... I find it hard to believe that you took computer science when you could not figure out how to talk to the mods/admin

Have you not noticed some of the profanity prone partners of yours that are no longer here?

You think computer cookies are the flavor of Gravity?

You're among the DM buffs here who thinks gravity can segregate DM from Observable matter & that Einstein was just clueless about the Laws of Gravity in his GR, but you DM buffs can't come up with the counter differential equations by which he proved he was right.

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